The thin membrane of the lungs provides an easily penetrated, convenient and generally safe means for obtaining rapid absorption of medication by the body. This is especially desirable where the lungs themselves are diseased or injured. Such medication or drugs are generally delivered to the lung membrane in the form of a fine mist or aerosol which is breathed into the lungs through the nose or mouth of the patient. A variety of devices, called nebulizers by those skilled in the art, have been developed for converting liquids into fine aerosols for this purpose. The simplest of these devices is the hand-held atomizer which converts a liquid to an aerosol when a bulb is compressed to produce a jet of air which atomizes the medication and propels it out of the atomizer. To be effective, the aerosols need to be provided at high concentrations and with droplet size in the respirable range (mass median aerodynamic diameter less than 5 micrometers).
Nebulizers are particularly useful for initiating and continuing respiratory therapy in conjunction with respirators, mechanical ventilators or breathing machines (hereinafter referred to generically as respirators) used to ventilate the lungs of patients having serious respiratory impairment. While some respirators incorporate nebulizers in their design, many do not. Nebulizers incorporated into the structure of such respirators often suffer from many disadvantages. One such disadvantage is severely limited capacity for medication to be nebulized, requiring frequent interruptions in the therapy as new medication is added to the nebulizer reservoir.
Another apparent disadvantage in such existing systems is the lack of a positive means for stirring the medication. This is particularly important to prevent settling when the liquid medication is a suspension. However, such stirring must not be so violent as to create turbulence capable of preventing or destroying nebulization.
Finally, some nebulizers are designed to operate continuously. Obviously this wastes both high pressure gas and medication, since the patient receives a benefit only during the inhalation phase. Those nebulizers which are designed to operate intermittently, i.e. only during the inhalation phase, are generally triggered by the movement of gas through the respirator during inhalation. This results in a slight delay in delivering medication to the patient, since some non-medicated gas will pass into the lungs before the nebulizer begins to operate. Thus, the patient does not receive the maximum possible amount of medication during the inhalation phase.
Most, if not all, such nebulizers are incorporated in respirators in which the inhalation and exhalation phases of the breathing cycle are triggered by changes in air pressure caused by the patient himself. Such "demand" respirators are not useful for patients whose respiratory systems are paralyzed and incapable of causing even slight changes in air pressure. These patients are aided by mechanical respirators in which the phases of the breathing cycle are triggered by electrical signals. There is now no convenient means of treatment for patients on such respirators.
Thus, the need exists for a nebulizer which can be attached to a mechanical respirator, especially those in which the breathing cycle is controlled by an electrical signal, which has a reservoir capacity sufficient to enable several hours of continuous treatment, which can prevent the settling of suspensions or mixtures without creating nebulization-destroying turbulence, and which can deliver medication to the patient just as the inhalation phase of the breathing cycle begins to insure that the patient will receive a maximum amount of medication during the inhalation phase without undue waste.